One special feature offered in mobile communications systems is group communication. The term “group”, as used herein, refers to any logical group of three or more users participating in the same group communication, e.g. a speech call. The same user may be a member of more than one communication group. Often the members of the communication group belong to the same organization. Also, typically, the same organization has several separate groups, i.e. a set of groups.
Push-to-talk over Cellular (PoC) is an overlay speech and data service in a mainly for mobile cellular network where a connection between two or more parties is established (typically) for a long period but the actual radio channels at the air interface are activated only when somebody is talking. This corresponds to the usage in traditional radiotelephones where the used radio frequency is agreed between the parties (e.g. military/police radios, LA radios, walkie-talkie-type radios). A PoC communication is not limited to mobile cellular network as users may use broadband, fixed or WLAN connections for communications. A push-to-talk switch, a voice activity detector (VAD) or any suitable means are used for indicating the user's desire to speak, and user equipment sends a service request to the network. The network either rejects the request or allocates the requested resources on the basis of predetermined criteria. At the same time, a connection is also established to a receiving user, or users in the case of group communication. After the voice connection has been established, the requesting user can talk and the other users can listen. When the user releases the push-to-talk switch or, in the case of traffic inactivity, the event is detected in the network, and the resources may be released and/or the talk item may be granted to another user. Thus, the resources are reserved only for the actual speech transaction or speech item, instead of reserving the resources for a “call” or session.
In some approaches, the group communication service, and also a one-to-one communication, is provided in form of a user or application level service so that the underlying communications system only provides the basic packet-mode connections (i.e. IP connections) between the group communications applications in the user terminals and the group communication service. The group communication service can be provided by a group communication server system in the infrastructure while the group client applications reside in the user equipments or terminals. For instance, the Voice over Internet Protocol (VoIP) enables a speech communication over an IP connection. The Session Initiation Protocol (SIP) is conventionally used for call establishment in “VoIP” based communication systems.
The group communication server system manages groups and lists (e.g. contact and access lists) that are needed for the group communication service. These lists are often referred to as resource lists. Functions provided by the server system may include providing list management operations to create, modify, retrieve and delete groups and lists, and providing storage for groups and lists. Users may have access to different lists in the server system, e.g., contact lists, group lists, etc. Most list management functions, such as adding or removing contacts or groups, take place as a direct result of a user action. Push-to-talk over Cellular (PoC) specifications defined by Open Mobile Alliance (OMA) can be found at http://www.openmobilealliance.org. A PoC participant who has authority to initiate and administrate an active group session, is called a PoC host or a group communication host herein.
The group communication (e.g. PoC, Push to Talk) referred to above, may be considered as a subset of the conferencing concept defined by Internet Engineering Task Force (IETF). IETF specifications and Internet Drafts can be found at http://www.ietf.org. Mechanism for policy manipulation of a multi-party conference is described in the document: An Extensible Markup Language (XML) Configuration Access Protocol (XCAP) Usage for Resource Lists, http://www.ietf.org/internet-drafts/draft-ietf-simple-xcap-list-usage-02.txt, October 2003, Work in Progress. Also in Push-to-Talk over Cellular concept, resource lists for group communication are preferably defined in the form of Extensible Markup Language (XML) structures, and thus XCAP can be used for storing and manipulating, e.g. creating, modifying and deleting, XML data on a server. The XCAP is a HTTP 1.1 based protocol that allows clients to read, write, modify and delete application data stored in XML format at a server. XCAP maps XML document elements and attributes to HTTP URIs that can be directly accessed by HTTP.
The participation in PoC sessions is only permitted once the user has applied for and been granted a subscription to access PoC services. The user can then participate in PoC sessions, either with another PoC user or with a PoC group. As a PoC participant, the user can be a member of more than one group at a time. The user is able to receive notifications of PoC groups available to participate in and hence to request to join those groups, or he may receive invitations to participate in other PoC groups. He is able to identify which group he is participating in and retrieve a list of PoC group members participating in each group. Changes in group status are propagated to the PoC participants, for instance, when a new user joins a group or when an existing user leaves a group.
Then number of groups in the system will be high, and the new groups will be created and old ones deleted all the time. There is a need for a mechanism for a group host to advertise a created or modified group.